Many current commercial electronic devices usually require different voltage levels as power sources. Thereby, charge pumps are disposed for using existing voltages to generate different voltage levels. For generating higher voltage levels, multiple stages of charge pumps are connected in series for attaining multiplying voltages. Nonetheless, given the limit by the efficiency of each stage of the charge pumps, the efficiency of multiplying voltages is insufficient, leading to inability of supplying large transient currents.
In addition, take applying power supplies to liquid-crystal displaying devices as an example. After liquid crystal materials are discovered in Europe, their utility is developed in the US. In Japan, their physical properties and application technologies in various fields are researched and new-generation liquid crystal display (LCDs) are developed continuously. At present, various liquid crystal technologies have been applied to displays extensively, particularly LCDs. Manufacturers have extended from the twisted-nematic LCD (TN LCD) to the super-twisted-nematic LCD (STN LCD), and further to the thin-film-transistor LCD (TFT LCD) with the trend of increasing scale. Accordingly, the research and development of the driving and power circuits of liquid-crystal displaying devices have become one of the key points for improving their resolution.
In general, the driving methods of liquid-crystal displaying devices can be divided into active and passive driving methods. No matter active or passive driving method, the scan electrode of the driving chip requires a high voltage. In order to simplify the external power circuit, a voltage boosting circuit is usually disposed in the power circuit of the displaying device. The voltage boosting circuit is normally composed of multiple stages of charge pumps connected in series for achieving the effect of providing high voltages.
In the past several years, display technologies have developed rapidly; the resolution of displays and the number of scan electrodes get higher increasingly. The part in a driving chip consuming more power is the transient when the scan electrode changes from the low voltage to the high voltage. According to the zero-capacitor architecture adopted by the voltage boosting circuit of the power supply of current displaying devices, higher voltage is given by multiplying the voltage directly. Given the limit imposed by the efficiency of each stage of charge pumps, the efficiency of multiplying voltages is insufficient, leading to inability of the voltage boosting circuits in supplying driving chips with large transient currents. When the loading requires a large transient current, the voltage boosting circuit cannot supply the required current. Besides, the output voltage of the voltage boosting circuit cannot be maintained within a stable range, resulting in incapability of meeting the requirement for high resolution. Hence, a novel architecture is required for driving the high-resolution driving chip using minimum number of capacitors.
Accordingly, the present invention provides a power circuit having multiple stages of charge pumps, which requires no floating capacitor for supplying large transient currents.